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Data Set ID:
RRRAG4

Radiostratigraphy and Age Structure of the Greenland Ice Sheet, Version 1

This data set contains the traced deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected by The University of Kansas Improved Coherent Radar Depth Sounder (ICORDS), Advanced Coherent Radar Depth Sounder (ACORDS), Multi-Channel Radar Depth Sounder (MCRDS), and Multichannel Coherent Radar Depth Sounder (MCoRDS) instruments between 1993 and 2013. This is an IceBridge-related data set.

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Geographic Coverage

Parameter(s):
  • Glaciers/Ice Sheets > Ice Sheets > Age at Ice-Thickness-Normalized Depths
  • Glaciers/Ice Sheets > Ice Sheets > Age of Internal Reflections
  • Glaciers/Ice Sheets > Ice Sheets > Depth at Specific Ages
  • Glaciers/Ice Sheets > Ice Sheets > Geometry of Internal Reflections
Spatial Coverage:
  • N: 81.51, S: 58.91, E: 6.62, W: -88.33

Spatial Resolution:
  • Varies x Varies
Temporal Coverage:
  • 23 June 1993 to 26 April 2013
Temporal Resolution: Varies
Data Format(s):
  • NetCDF
  • MATLAB
  • XML
Platform(s) DC-8, P-3B
Sensor(s): ACORDS, ICORDS, MCRDS, MCoRDS
Version: V1
Data Contributor(s): Joseph MacGregor, Mark Fahnestock, Ginny Catania, John Paden, Prasad Gogineni, S. Young, Susan Rybarski, Alexandria Mabrey, Benjamin Wagman

Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

MacGregor, J. A., M. Fahnestock, G. Catania, J. Paden, P. Gogineni, S. K. Young, S. C. Rybarski, A. N. Mabrey, B. M. Wagman, and M. Morlighem. 2015. Radiostratigraphy and Age Structure of the Greenland Ice Sheet, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/UGI2BGTC4QJA. [Date Accessed].

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Detailed Data Description

Format

The data files are HDF5-compliant MATLAB (.mat) and NetCDF (.nc) formats. The NetCDF file was generated using MATLAB R2015a and is v4.1.3 compliant.

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File and Directory Structure

Data are available in the https://n5eil01u.ecs.nsidc.org/ICEBRIDGE/RRRAG4.001/ directory.

Note: Please note that the data are located in a directory named /1993.06.23/. However the data temporal coverage includes 23 June 1993 to 26 April 2013.

The data file is paired with an associated XML file. XML files contain point latitudes and longitudes, and file and campaign metadata.

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File Naming Convention

File names:

RRRAG4_Greenland_1993_2013_01_age_grid.nc

RRRAG4_Greenland_1993_2013_01_radiostratigraphy.mat

RRRAG4_LLLLL_YYYY_yyyy_XX_NNNN.xxx

Where:

Table 1. File Naming Convention
Variable Description
RRRAG4 Short name for Radiostratigraphy and Age Structure of the Greenland Ice Sheet
LLLLL Location, e.g. Greenland
YYYY_yyyy Span of years represented in data set, e.g. 1993 to 2013.
XX Local version id
NNNN Data file contents, e.g. grid, radiostratigraphy
XXX Indicates file type, e.g. NetCDF (.nc), MATLAB (.mat)
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File Size

The RRRAG4_Greenland_1993_2013_01_age_grid.nc data file is approximately 2.2 GB.

The RRRAG4_Greenland_1993_2013_01_radiostratigraphy.mat data file is approximately 1.4 GB.

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Volume

The entire data set is approximately 3.6 GB.

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Spatial Coverage

Spatial coverage for the Radiostratigraphy and Age Structure of the Greenland Ice Sheet data includes Greenland.

Greenland:
Southernmost Latitude 58.91° N
Northernmost Latitude: 81.51° N
Westernmost Longitude: -88.33° W
Easternmost Longitude: 6.62° E

Spatial Resolution

Spatial resolutions are variable. The horizontal posting of the radar data is of the order of 10 m. Vertical range resolution of the ice-penetrating radar systems used are of the order of meters, but internal reflections were typically traced at no finer than 10 m. The horizontal resolution of the gridded age structure and isochrone depths is 1 km. The vertical resolution of the age structure is ice–thickness–dependent, for example for a 2 km ice column, the vertical resolution of the age volume is 1/25th of that, or 80 m.

The nominal vertical range resolution in ice of these data is 2.5 m to 4.4 m and their along-track horizontal resolution varies between 15 m and 150 m, depending on the system used and whether the data were focused using synthetic aperture radar (SAR) techniques.

Projection and Grid Description

The radar data are projected using the NSIDC Sea Ice Polar Stereographic North projection EPSG:3413. WGS84 ellipsoid, a standard parallel of 70°N, and a false central meridian of 45°W and sets both the northing and easting origin as the North Pole. Other Greenland data sets also used in this study are re-projected onto EPSG:3413.

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Temporal Coverage

23 June 1993 to 26 April 2013

Temporal Resolution

Semi-annual from 1993 to 2013. Survey campaigns typically occurred over several weeks during the boreal spring/summer (March to July).

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Parameter or Variable

Parameter Description

The gridded data file contains fields as described in Table 1.

Table 1. Gridded Data Parameter Description
Parameter Description Units
age_iso Age of selected isochrones Years
age_norm Age at ice-thickness-normalized depths, evenly spaced vertically Years
age_norm_uncert Age uncertainty at ice-thickness-normalized depths, evenly spaced vertically Years
depth_iso Depths of selected isochrones Meters
depth_iso_uncert Depth uncertainty of selected isochrones Meters
depth_norm Ice-thickness-normalized depth of vertical layers Depth as fraction of ice thickness
num_age_iso Number of isochrones

Count

num_depth_norm Number of vertical layers Count
thick Ice thickness Meters
x x-dimension grid centered on Greenland Kilometers
y y-dimension grid centered on Greenland Kilometers

The HDF5 traced radiostratigraphy data file contain fields as described in Table 2.

Table 2. Radiostratigraphy Data File Parameter Description
Parameter Description Units
age reflection age Year
age_uncert reflection age uncertainty Year
distance distance along segment Kilometers
echo_intensity ice depth to reflection Decibels
elevation layer elevation referenced to GIMP Meters
elevation_bed bed elevation referenced to GIMP Meters
elevation_surface surface elevation referenced to GIMP Meters
latitude latitude Degrees
longitude longitude Degrees
time_gps measurement time since 1 January 0000 Seconds
thickness ice thickness Meters
traveltime traveltime to traced reflection Seconds
traveltime_surface traveltime to surface Seconds
x x value in EPSG:3413 Kilometers
y y value in EPSG:3413 Kilometers

Sample Data Record

See NASA's Scientific Visualization Studio for a visualization of the Greenland Ice Sheet stratigraphy.

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Software and Tools

The following external links provide access to software for reading and viewing HDF5 and netCDF data files. Please be sure to review instructions on installing and running the programs.

HDF Explorer: Data visualization program that reads Hierarchical Data Format files (HDF, HDF-EOS and HDF5) and also netCDF data files.

Panoply netCDF, HDF and GRIB Data Viewer: Cross-platform application. Plots geo-gridded arrays from netCDF, HDF and GRIB data sets.

For additional tools, see the HDF-EOS Tools and Information Center.

MATLAB files may be opened using MATLAB or the Octave high-level language.

See also: MATLAB scripts/functions for tracing reflectors in ice-penetrating radar data.

Quality Assessment

Data were quality controlled using multiple analysts, network graphs, and various other checks, especially to detect and resolve vertical overturning in the radar–inferred depth–age relationship.

The radiostratigraphy recorded within these radar data varies in quality depending on the system used and the area of the ice sheet surveyed. The overall quality of these radar data has improved over time as newer radar systems were developed and deployed. See MacGregor et al. 2015 for additional details on quality control methods.

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Data Acquisition and Processing

Theory of Measurements

See Gogineni et al. 1998 for a review of the theory and methodology underlying the collection of coherent ice-penetrating radar data.

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Data Acquisition Methods

The two-way travel times of the air–ice and ice–bed reflections were measured by University of Kansas personnel throughout the acquisition period, for example Gogineni et al. 1998, and these travel times were used without further modification. The reflections were traced manually using a MATLAB-based interface.

These data include 512 transects of varying lengths (6–3965 km; median 530 km).

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Derivation Techniques and Algorithms

The investigators examined the 479,595 km of 150 MHz and 195 MHz ice-penetrating radar data collected over the Greenland Ice Sheet by the University of Kansas between 1993 and 2013.

As described in MacGregor et al. 2015, core-intersecting reflections were dated using synchronized depth–age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection–inferred depth–age relationships using the local effective vertical strain rate. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly.

Figure 1 outlines the system designs, acquisition parameters, and processing techniques applied to the data. Please refer to MacGregor et al. 2015 for full details on each processing step. Section numbers (§) noted in Figure 1 refer to sections in MacGregor et al. 2015.

Figure 1. Key Steps and Order of Operations for (a) Tracing, (b) Dating, and (c) Normalizing the Radiostratigraphy (MacGregor et al. 2015).

Trajectory and Attitude Data

Transect locations are given in both geographic and projected coordinates, along with elevations as given. Corrected elevations are also provided so the surface elevation inferred from the ice–air reflection and the aircraft is consistent with the Greenland Ice Mapping Project (GIMP) Digital Elevation Model (DEM).

Processing Steps

The radar data were typically SAR focused. Data were traced at the highest available processing level.

Error Sources

The primary potential error sources include errors in tracing and dating the radiostratigraphy contained within these data sets. Errors in tracing, for example an incorrectly traced reflection or an incorrectly matched pair of discontinuous reflections, produce structural uncertainty in subsequent analyses including dating and gridding that cannot easily be quantified. Such errors will be resolved as they are identified and addressed in later revisions of these data products. Uncertainty in dating is quantified following MacGregor et al. 2015, both for individual reflections and the gridded products, and it represents the best estimate of the error in this aspect of the data set. It is a function of the age uncertainty reported for the ice–core depth–age scales and the degree of interpolation and extrapolation necessary to reach any given point in the ice sheet.

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Sensor or Instrument Description

The radar systems used were designed to sound the entire ice thickness and to detect internal reflections close to the bed. See CReSIS rds_readme.pdf for further instrument details.

ICORDS: Improved Coherent Radar Depth Sounder, 1993 to 2002

ICORDS: Bandwidth: 141.5-158.5 MHz, Tx power: 200 W, Pulse duration: 1.6 us, Waveform: Analog chirp generation (SAW), Acquisition: Single channel 8 bit ADC, 18.75 MHZ IQ sampling (coherent averaging, but incoherent recording only), Dynamic Range: Sensitivity timing control, Rx aperture: 2 wavelengths (4 dipoles), Tx aperture: 2 wavelengths (4 dipoles), Bistatic Rx/Tx, Data rate: ~0.05 MB/sec.

ICORDS2: Bandwidth: 141.5-158.5 MHz, Tx power: 200 W, Pulse duration: 1.6 us, Waveform: Analog chirp generation (SAW), Acquisition: Single channel 12 bit ADC, 18.75 MHz IQ sampling, Dynamic Range: Sensitivity timing control, Rx aperture: 2 wavelengths (4 dipoles), Tx aperture: 2 wavelengths (4 dipoles), Bistatic Rx/Tx, Data rate: ~0.5 MB/sec.

ACORDS: Advanced Coherent Radar Depth Sounder, 2003 to 2005

Bandwidth: 140-160 MHz, Tx power: 200 W, Waveform: Single channel chirp generation, Acquisition: Single channel, Dynamic Range: low and high gain channels, Rx aperture: 2 wavelengths (4 dipoles), Tx aperture: 2 wavelengths (4 dipoles), Bistatic Rx/Tx, Data rate: 20 MB/sec.

MCRDS: Multi-Channel Radar Depth Sounder, 2006 to 2009

MCRDS: Bandwidth: 140-160 MHz, Tx power: 800 W, Waveform: Single channel chirp generation, Acquisition: Eight channels, 12 bit ADC at 125 MHz bandpass sampling, Dynamic Range: waveform playlist, Rx Aperture: 3 wavelength aperture (6 dipoles), Tx Aperture: 3 wavelength aperture; but configurable for ping-pong operation (6 dipoles), Bistatic Rx/Tx, Data rate: 30 MB/sec total.

MCRDS on P3: Bandwidth Selection: 140-160 MHz or 435-465 MHz, Rx Aperture: 2 wavelength aperture (4 dipoles), Tx Aperture: 2 wavelength aperture (4 dipoles).

Multichannel Coherent Radar Depth Sounder (MCoRDS), 2010 to 2013

Bandwidth: 180-210 MHz (DC-8 platform restricted to 189.15-198.65 MHz), Tx power: 550 W, Waveform: Eight channel chirp generation, Acquisition: Eight channels, 14 bit ADC at 111 MHz bandpass sampling, Dynamic Range: waveform playlist, Rx Aperture: 1.5 wavelength aperture, Tx Aperture: 1.5 wavelength aperture; fully programmable, Monostatic Rx/Tx, Data rate: 12 MB/sec per channel.

MCoRDS on DHC-6 Twin Otter (v1), Bandwidth: 140-160 MHz, Tx power: 500 W, Rx Aperture: 3 wavelength aperture, Tx Aperture: 3 wavelength aperture; fully programmable, Bistatic Rx/Tx.

MCoRDS on P3-B Orion: Bandwidth: 180-210 MHz (EMI restricted to 10 MHz within 180-210 MHz most segments), Tx power: 600 W, Acquisition: Sixteen channels (multiplexed on to 8 channels), 14 bit ADC at 111 MHz bandpass sampling, Rx Aperture: 2 wavelength, 3.5 wavelength, and 2 wavelength apertures, baseline of 6.4 m between each aperture, Tx Aperture: 3.5 wavelength aperture; fully programmable, Mixed monostatic and bistatic tx/rx, Data rate: 6 MB/sec per channel.

MCoRDS on Douglas DC-8: Dynamic Range: waveform playlist coupled with low gain and high gain channels.

MCoRDS on DHC-6 Twin Otter (v2): Tx power: 500 W, Acquisition: Sixteen channels (multiplexed on to 8 channels), 14 bit ADC at 111 MHz bandpass sampling, Rx Aperture: Two 3 wavelength apertures with 13.8 m baseline.

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References and Related Publications

Contacts and Acknowledgments

Joseph A. MacGregor
Research Physical Scientist
NASA Goddard Space Flight Center
Cryospheric Sciences Laboratory (Code 615)
Greenbelt, MD 20771

Acknowledgments: 

NSF (ARC 1107753 and 1108058; ANT 0424589) and NASA (NNX12AB71G) supported the generation of this data set. Several organizations (Program for Arctic Regional Climate Assessment, Center for Remote Sensing of Ice Sheets and Operation IceBridge) and innumerable individuals supported and performed the collection and processing of the radar data used to generate this data set. The NASA Advanced Supercomputing Division permitted the use of the Pleiades Supercomputer for kriging the radiostratigraphy.

Document Information

Document Creation Date

07 August 2015

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No FAQs or How Tos available for this data set.

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